The long term goal of this fellowship project is to be able to provide clinical intervention to patients suffering from salivary gland loss of function. Parotid gland dysfunction affects millions of people across the nation, and stems from several causes. Sjogren's syndrome (which affects 2 - 4 million Americans), for instance, results in hypofuction of the gland. Also, radiation damage severely affects the parotid gland and is common among patients receiving treatment for head and neck carcinomas. Loss of function in patients results in chronic xerostomia. This leads to a reduction in quality of life for these patients as well as a reduction in overall oral health as the incidence of dental caries and periodontal disease increases. The ability to regenerate or restore function to damaged parotid glands would greatly increase patient health and quality of life. This requires further knowledge of how the gland develops and differentiates into its different cell types. Defining the molecular mechanisms of parotid differentiation is a significant goal. Specifically, the parotid acinar cells are responsible for producing and secreting the salivary proteins amylase, parotid secretory protein (PSP), and others in response to parasympathetic nerve stimulation. Parotid salivary proteins contribute to defense against bacteria and yeast, and initiation of digestion. These cells are highly specialized; however, the terminal differentiation of this cell type is poorly understoo. Within the last decade, the importance of microRNAs on the process of development and differentiation has been identified in many cell types. This suggests that microRNAs are a common mechanism used by the cell to control differentiation. However, the role of microRNAs in acinar terminal differentiation has yet to be explored. It remains to be investigated if microRNA levels correlate with acinar differentiation in vivo, and which microRNAs are important. This project addresses the hypothesis that microRNA expression drives gene networks that are important for parotid acinar differentiation, through two separate aims. Aim one is to determine if microRNAs are differentially expressed during parotid acinar differentiation in vivo and as compared to undifferentiated acinar cells. And to identify potential microRNA target genes and networks. MicroRNA (and well as mRNA) levels will be measured throughout the course of parotid acinar differentiation in the rat, with the goal of using bioinformatics techniques to identify potentially biologically relevant miRNA:mRNA interactions and gene regulatory networks. Aim 2 will experimentally test the function of the predicted interactions by determining if microRNAs drive expression of differentiation associated gene networks in parotid acinar cells. This project contributes to the long term goal of understanding salivary gland biology to the point that clinical interventions can be developed to regenerate or restore glands to those patients suffering from parotid hypofunction.